1. Field of the Invention
The present invention relates to a method of detecting foreign matter or materials in pulp suspension and a device for detecting the same.
2. Description of the Related Art
In a papermaking process, foreign matter or materials mixed with paper materials causes paper break (break deteriorates operational performance of a paper machine and increases in the production cost) and deteriorates the quality of paper as a commercial product, and consequently, foreign matter in pulp suspension is removed by using a screen, a cleaner, or the like. It is important to check the state of foreign matter in the pulp suspension (such as whether a large amount of foreign matter is present, or the like) which is fed to the papermaking process.
Thus, conventionally, the state of foreign matter, such as dust, contained in the pulp suspension is checked by the following method. The pulp suspension per se is extracted and a handmade sample sheet is produced from the extracted pulp suspension. Foreign matter in the sample sheet is counted, or foreign matter in paper as a finished product is counted.
However, in this method, feedback to the machine in the papermaking process is delayed, and thus, a quick response is not achievable.
In order to overcome the above drawbacks, the following method is available in these days. Light is ejected to the pulp suspension per se, and the resulting reflected light is detected and processed.
In such a method, approximately 1% concentration of the pulp suspension enables the detection of foreign matter such as dust, or the like.
However, when the pulp suspension is highly concentrated, it is difficult to distinguish foreign matter, such as dust, from effective fiber, thus lowering measuring precision.
If the pulp in the pulp suspension is bleached, the effective fiber and foreign matter in the pulp suspension can be distinguished by the difference of colors (the contrast of colors). However, when the pulp suspension material is waste paper, corrugated board, or the like, it is hard to distinguish foreign matter from effective fiber in the pulp suspension, thus lowering measuring precision.